Ketal Claisen Rearrangements of Simple Aliphatic Ketals

Article abstract of DOI:10.1021/jo00170a002

The ketal Claisen rearrangement has been studied with eight simple unsymmetrical ketals in order to establish the regioselectivity associated with the transformation.Three different allylic alkohols were examined.Carbon-carbon bond formation on the more highly substituted branch of the parent ketone generally predominated over substitution on the less highly substituted branch.However, additional substituents on the α or β carbons of the ketal lower the selectivity substantially.Extensive β substitution can completely reverse the normal selectivity.The rection is relatively insensitive to the concentration of the weak acid catalyst.The yields range between 27 and 84 percent, and the products have been characterized.A model that accounts for the observations is also described.